Purpose: There is evidence suggesting that visual disturbances in patients with Alzheimer's Disease (AD) are due to pathologic changes in the retina and optic nerve, as well as to higher cortical impairment. The purpose of this study was to evaluate retinal hemodynamic parameters and to characterize patterns of retinal nerve fiber layer (RNFL) loss in patients with early AD.
Methods: Nine patients with mild to moderate probable AD (mean Mini Mental State Examination score 24 of a possible 30 (age 74.3 +/- 3.3 years; mean +/- SD) and eight age-matched control subjects (age, 74.3 +/- 5.8 years) were included in this prospective cross-sectional study. Blood column diameter, blood velocity, and blood flow rate were measured in the major superior temporal retinal vein in each subject by using a laser Doppler instrument. Peripapillary RNFL was measured by optical coherence tomography.
Results: Patients with AD showed a significant narrowing of the venous blood column diameter (131.7 +/- 10.8 microm) compared with control subjects (148.3 +/- 12.7 microm, P = 0.01), and a significantly reduced venous blood flow rate (9.7 +/- 3.1 microL/min) compared with the control subjects (15.9 +/- 3.7 microL/min, P = 0.002). A significant thinning of the RNFL was found in the superior quadrant in patients with AD (92.2 +/- 21.6 microm) compared with control subjects (113.6 +/- 10.7 microm, P = 0.02). There were no significant differences in the inferior, temporal, or nasal RNFL thicknesses between the groups.
Conclusions: Retinal abnormalities in early AD include a specific pattern of RNFL loss, narrow veins, and decreased retinal blood flow in these veins. The results show that AD produces quantifiable abnormalities in the retina.